Why does Christmas always fall on Thursday in the leap year halfway between two odd-numbered years with Christmas on Sunday?

Answer 1

There is a pattern in the way days and dates fall. If Christmas Day is on a Sunday 3 years before a leap year, then it will always follow that the Christmas Days in the next years are a Monday, a Tuesday, and for the leap year Wednesday will be skipped and Christmas Day will be on a Thursday. Follow on for another 3 years and you get Friday, Saturday and Sunday. Leap years are always even, so if it is 3 years before a leap year, then the first year that the Sunday is on has to be odd, as will the year 3 years after a leap year. These patterns are common and you could look at other specific combinations of dates and days in the same way and find recurring patterns there too.

Answer 2

Century leap years happen every 400 years, and the Gregorian calendar completely repeats itself every 400 years.